Lubricants or lubricating media are used in a wide variety of bearings. Providing a bearing with an optimal supply of lubricant can protect the bearing from a variety of harmful influences and may increase the service life of the bearing. When the bearing operates, the lubricant is exposed to different loads or forces which may cause the lubricant to break down or deteriorate. For example, the lubricant may be subject to wear. Furthermore, contaminants or foreign bodies can accumulate in the lubricant. In addition, a quantity of lubricant in the bearing can change during operation. For example, the quantity of lubricant can increase when the bearing is relubricated and can decrease if lubricant leaks or escapes from the bearing.
In order to maintain a quality and/or quantity of lubricant in a bearing, the lubricant is usually replaced or supplemented. For this purpose different conventional lubricating systems or concepts can be employed. For example, in some conventional lubricating systems the lubricant of the bearing is completely replaced during scheduled maintenance work, at an interval that is set or suggested by the manufacturer, for example. In this way the quantity of lubricant can be held constant under certain conditions. However, the complete replacement of all lubricant at planned intervals means that the quality of the lubricant will periodically be at a high level and thereafter decrease substantially continuously until the next replacement is due. In other words, the quality of the lubricant generally falls between replacements.
Alternatively the bearing may be lubricated using a conventional centralized lubrication system. Conventional centralized lubrication systems introduce a partial quantity of lubricant, small in relation to the total quantity of lubricant of the bearing, into the bearing, usually at defined intervals. Usually the bearing then includes lubricant escape openings from which old or used lubricant escapes when new or fresh lubricant is introduced. The lubricant quality can usually be held at a relatively uniform level by the regular addition of fresh lubricant. However, a quantity of lubricant in the bearing cannot be precisely determined, because it is difficult to precisely control the amount of lubricant that escapes from the bearing when new lubricant is added.